Can a single object in an array be exported?
To avoid unexpected behaviours, it's better to duplicate the object (Shift D) and apply the array modifier.
Then in edit mode there are several ways of fast selecting, some of them:
B to box select, C to paint select, L to select all the area where the mouse is hovering, Ctrl L to select all the geometry linked to the selected area, H to hide every unwanted or occluding geometry, Ctrl I to invert the selection, vertex groups select/unselect buttons (if there are vertex groups), Alt left click to select loops, ....
When all the desired area is selected you can press P to separate it into a new object and delete the duplicate.